As you know, the BPMN2 Modeler uses Graphiti to render the BPMN2 model objects. This framework requires, at a minimum, an SWT Composite to do its rendering so it's not possible to get an image without opening some kind of viewer. It may be possible to open the BPMN2 Modeler editor and have it hide the Composite somehow, generate the image file, and immediately close the editor. If you figure out a way to do that, please let me know

My problem is to include extended pattern (problem of add new workflow pattern) into bpmn file. My solution for this problem is a java application witch the user select desired pattern to insert automatically into bpmn file. And I would like to show an image of new bpmn diagram after the insertion of the pattern.

That is going to be difficult. Is it possible to just do a screen capture of the workflow pattern and use that as the image? I know you would have to prepare images of all the patterns you will be supporting, but it's easier than writing a graphiti viewer and doing a "Save image".